1. Field of the Invention
The present invention relates generally to an apparatus and method for receiving signals in a communication system, and in particular, to an apparatus and method for receiving signals by buffering Log-Likelihood Ratio (LLR) values according to a mapping scheme.
2. Description of the Related Art
A signal receiving apparatus of a communication system includes a receiver, a demapper, a deinterleaver, and a decoder. The decoder is realized with a Convolutional Turbo Code (CTC) decoder or a Convolutional Code (CC) decoder. The reason why the decoder is realized with the CTC decoder or the CC decoder is because the communication system can basically use the CC decoder and optionally use the CTC decoder.
A signal transmitting apparatus of the communication system includes an encoder, an interleaver, a mapper, and a transmitter. The encoder is realized with a CTC encoder or a CC encoder. If there are information data bits to transmit in the signal transmitting apparatus, the information data bits are delivered to the encoder. The encoder encodes the information data bits into coded bits according to a preset encoding scheme, and outputs the coded bits to the interleaver. The interleaver interleaves the coded bits according to a preset interleaving scheme, and outputs the interleaved bits to the mapper. The mapper maps the signal output from the interleaver according to a preset mapping scheme, and outputs the mapped signal to the transmitter. The transmitter performs a transmission process on the signal output from the mapper, and transmits the signal to the signal receiving apparatus.
To recover the information data bits in the signal receiving apparatus, the receiver performs a reception process on a received signal, and outputs the signal to the demapper. The demapper demaps the signal output from the receiver according to a demapping scheme corresponding to the mapping scheme used in the mapper, and outputs the demapped signal to the deinterleaver. It is assumed herein that the demapper uses an LLR scheme. The deinterleaver deinterleaves the signal output from the demapper according to a deinterleaving scheme corresponding to the interleaving scheme used in the interleaver, and outputs the deinterleaved signal to the decoder. The decoder decodes the signal output from the deinterleaver according to a decoding scheme corresponding to the encoding scheme used in the encoder to restore the received signal to its original information data bits. Because the demapper uses the LLR scheme as stated above, the signal output from the demapper, i.e., the LLR values, should be buffered in a buffer before being deinterleaved in the deinterleaver. Because a buffering operation of the LLR values may considerably affect the performance of the communication system, the buffer must be designed to take into account a delay time caused by the buffering of the LLR values. In addition, the buffer should be designed to take into account not only the delay time but also the size and cost of the signal receiving apparatus.
Currently, however, there is no proposed operation and structure of a buffer for buffering the LLR values in the BWA communication system. Accordingly, there is a need for a scheme of receiving signals by buffering LLR values in the BWA communication system.